1. Field of the Invention
The present invention relates to a vacuum pump that may avoid precipitate of gas molecular composition by heating a discharge path of gas effectively with a small amount of electrical power and is superior in handling property and safety aspect in low cost.
2. Description of the Related Art
Conventionally, a vacuum pump such as a turbo molecular pump or a screw groove type pump is well known. Such a vacuum pump has been extensively used for analysis and measurement utilizing electronic rays or in the case where a vacuum process such as a dry etching process or a CVD through a semiconductor manufacturing apparatus or a liquid crystal manufacturing process is performed by discharging process gas within the chamber.
In such a vacuum pump, a stator portion and a rotor portion are received in an outer sleeve portion having a hollow portion, and a flow path of gas is formed by means of the stator portion and the rotor portion. Then, the rotor portion is rotated by means of a motor to thereby move the gas of the flow path so as to suck the gas from the outside through an intake port.
Such a vacuum pump is a turbo molecular pump in which a plurality of spacers are arranged coaxially with the rotor portion, stator blades projecting toward the rotor portion are arranged between the spacers and rotor blades projecting between the stator blades are arranged in the rotor portion. In this turbo molecular pump, gas molecular is struck to be transferred by the rotation of the rotor blades.
In another example, a screw groove is formed in one of circumferential surfaces, facing each other, of the rotor portion and the stator portion, and a screw groove type vacuum pump for transferring the gas utilizing viscosity of the gas by the rotation of the rotor is used in combination with the turbo molecular pump. This is usually used in a semiconductor manufacturing apparatus or the like.
By the way, in the above-described vacuum pump, a pressure is low on the intake port side upon the suction of gas and a pressure is kept high on the discharge port side. Also, in order to prevent the excessive heating due to the provision of electronic equipments such as motors arranged in the central portion, the interior of the vacuum pump is kept at a temperature not higher than a predetermined temperature by means of a cooling means for recirculating water.
For this reason, in the case where reactive gas such as AlCl3 or the like being process gas is to be sucked in an etching process in the case where the pump is used in the semiconductor manufacturing apparatus, in some cases, the gas is precipitated by the sublimation of gas to be transferred in the vicinity of the discharge port to stick to the surface of the flow path.
Then, due to this deposition, there is a possibility that the flow of gas is prevented, the transfer efficiency of gas by the vacuum pump becomes low, or in the worst case, the depositions adhered to the rotor portion and the stator portion are brought into contact with each other to cause the damage of the members.
In the vacuum pump, as a technology for avoiding the precipitation due to the sublimation of the reactive gas by heating the flow path of gas, there is a conventional technology for arranging a heater using a nichrome line around the lower portion of the vacuum pump.
FIG. 9 is a schematic view representing an overview structure of the vacuum pump adopting such a technology.
The conventional vacuum pump shown in FIG. 9 is a composite pump. A stator portion 118 and a rotor portion 114 are received in an outer sleeve portion 116 having a hollow portion. The outer sleeve portion 116 and the stator portion 118 are fixed and supported onto a base 119. The rotor portion 114 is supported rotatably coaxially to the stator portion 118 on the base 119. Rotor blades 1141 projecting in a radial direction of rotation at one end in an axial direction are provided in a plurality of stages in the axial direction of rotation. The stator portion 118 is provided with a plurality of stator blades 1181 projecting from an outer side of the rotor portion 114 between the rotor blades 1141, and is provided with groove provided spacers 1180 surrounding the outer circumferential surface of the rotor portion 114 in the vicinity thereof at the other end of the axial direction.
Also, a temperature sensor 151 for detecting the temperature in the vicinity of the flow path of the gas is provided in the vicinity of the base 119. Also, a water-cooling pipe 171 is in contact with the bottom surface of the base 119. The water-cooling pipe 171 is adapted to be opened and closed by means of an electromagnetic valve 172. Furthermore, a nichrome heater 160 is wound around the outer circumferential surface of the base 119.
Then, the rotor portion 114 is rotated relative to the stator portion 118 by a motor disposed in the substantially center of the vacuum pump. The gas molecular is stuck down by means of the rotor blades 1141 and the stator blades 1181 on the side of the above-described end. On the other end side, the viscous flow of the gas molecular stuck down is formed in the groove provided spacers 1180 to transfer the gas molecular to the discharge port by the viscosity. Thus, the gas from the opening portion (suction port) on one end side of the outer sleeve portion 116 is discharged from the discharge port formed in the base 119 through the flow path of gas formed between the rotor portion 114 and the stator portion 118.
In this vacuum pump, as shown in FIG. 10, a decision is made as to whether a heater 160 and an electromagnetic valve 172 is turned on or off on a judgement device 185 on the basis of a set temperature Td set in advance and a temperature Tr detected from the temperature sensor 151 by means of a controller 180 on the basis of the output from a temperature sensor 151. Namely, if Tr less than Td, the heater 160 is turned on to heat the gas flow path, and the electromagnetic valve 172 is turned off to thereby stop the flow of water through the water-cooling pipe 171. Also, in the case where Trxe2x89xa7Td, the electromagnetic valve 172 is turned on so that the flow of water through the water-cooling pipe 171 is recirculated. The heater 160 is turned off so that the gas flow path is cooled down. Then, the flow path of gas is kept in the predetermined temperature range by means of the elevation of temperature by the heater 160 and the cooling-effect by the flow of water through the water-cooling pipe 171. Thus, the precipitation due to the sublimation of the reactive gas is controlled.
Also, as a technology for avoiding the precipitation of the gas composition in the vicinity of the discharge port, there is a proposal of the technology to heat the flow path of gas by providing an alternative current to a coil using magnetic material as a core (Japanese Utility Model Registration No. 2570575).
According to the technology, the flow path of gas is heated by means of the heat generation of the magnetic hysteresis and the heat generation within the core due to the eddy current by embedding a coil using the magnetic material as a core into the base supporting the outer sleeve and having the discharge port to feed alternating current to the coil.
However, in the vacuum pump using the heater shown in FIG. 9, the heating of the vicinity of the discharge port is performed only by means of the nichrome line heater 160. Accordingly, it is necessary to use a large capacity heater 160 at about 300 W. For this reason, there is a problem that a large load is applied to the controller power source, it is difficult to handle the vacuum pump since it is necessary to use a cable having a greater diameter, or the manufacturing cost and the running cost are high.
Also, in order to provide the heater 160 on the surface of the vacuum pump and heat the flow path of gas from the outside, the heat is likely to escape to the outside and it is impossible to give Joule""s heat effectively to the portion to be heated. Thus, there is a problem that a further large electric power is needed. Incidentally, in order to ensure the safety aspect, a method for covering the heater 160 by silicone rubber or the like is adopted, however, which leads to such a problem in that the manufacturing cost is further increased, the size is increased due to the necessity to provide the protection function such as thermostat or the like or the manufacturing cost is further increased.
Furthermore, in the vacuum pump using the heater shown in FIG. 5, it takes long time to cool down the nichrome line after the heater 160 is turned off, and the followability of temperature control is not good.
In the technology for feeding the alternating current to the coil having a core made of magnetic material and heating the flow path of gas, since the heat is generated by the magnetic hysteresis and the flow path of gas is heated from the vacuum pump interior portion by utilizing the heat generation due to the eddy current, it is possible to effectively utilize the heat generation with safety in comparison with the vacuum pump using the heater as shown in FIG. 5. However, it takes a structure in which the coil is embedded in the interior of the base of the pump, the excited heat is absorbed in the base, and it is difficult to elevate the temperature of the flow path portion only. Also, since the strong alternating magnetic field is generated in the interior of the vacuum pump, for example, in the case where a position sensor or the like for detecting the delicate change of the magnetic field in terms of the inductance change of the coil, the alternating magnetic field would adversely affect as noise, and in particular, in the magnetic bearing type vacuum pump, the adverse affect might be remarkable.
In order to solve the above-described problems, a first object of the present invention is to provide a less expensive pump that may avoid the precipitation of the gas molecular composition in a flow path of gas by heating the flow path of gas effectively with a small electric power. Also, in addition to the first object, a second object of the present invention is to provide a vacuum pump that is superior in handing property and safety aspect.
In order to attain the first object, according to the present invention, there is provided a vacuum pump (first structure) comprising: an outer sleeve portion; a stator portion received in a hollow portion of the outer sleeve portion; a rotor portion received rotatably relative to the stator portion within the hollow portion of the outer sleeve portion for forming a flow path of gas in cooperation with the stator portion; a motor for rotating the rotor portion and for moving the gas within the flow path; a base portion having a discharge path for discharging the gas from the flow path to the outside for supporting the stator portion; a heating electromagnet arranged in the vicinity of the discharge path; a magnetic member for forming a magnetic path of magnetic force by the heating electromagnet arranged in the vicinity of the discharge path; and a control means for controlling current supply to the heating electromagnet.
In the vacuum pump with the first structure of the present invention, when the heating electromagnet is subjected to the current supply by the control means, the coil of the heating electromagnet is heated. Also, the magnetic path of magnetic force by the heating electromagnet is formed through the magnetic member so that the magnetic affect by the heating electromagnet will no longer occur. Then, since the magnetic member is in intimate contact with the heating electromagnet, the heat generated within the coil of the heating electromagnet is rapidly transferred to the magnetic member. The magnetic member may quickly heat the gas because the member is provided within the flow path of gas.
Thus, in the vacuum pump with the first structure of the present invention, when the heating electromagnet is arranged in the vicinity of the discharge path of gas, furthermore, the magnetic member is brought into intimate contact with the heating electromagnet so as to form a magnetic path of magnetic force of this heating electromagnet and the heating electromagnet is subjected to the current supply, the Joule""s heat generated in the coil of the electromagnet is effectively transferred to the magnetic member. As a result, it is possible to heat the discharge path and effectively suppress the precipitation due to the sublimation of the reactive gas with a less electric power. In this case, the magnetic member may be formed integrally with the heating electromagnet. Then, since the electric power may be suppressed less, it is possible to reduce the load imposed on the control power source, to dispense with a thick cable, to easily handle, and to reduce the manufacturing cost or running cost.
The above-described heating electromagnet is arranged in the vicinity of the discharge path. This discharge path vicinity means the vicinity of the rotor portion and the stator portion out of the joint portion of the discharge path formed in the base with the gas flow path formed by the rotor portion and the stator portion and the discharge path formed in the base. The pressure is relatively high in the vicinity of the discharge path and the precipitation due to the sublimation of the reactive gas is likely to occur. However, according to this structure, it is possible to positively prevent the precipitation due to the sublimation of the reactive gas in this portion. Then, it is possible to prevent the degradation of the discharge function due to the prevention of the gas flow and the contact between the rotor portion and the precipitated material. Also, the current to be fed to the heating electromagnet may be a d.c. current to thereby avoid the generation of the noise due to the alternating magnetic field.
The above-described stator portion and the above-described base or the above-described outer sleeve portion and the base may be formed as the discrete members at the beginning and fixed together later, or formed integrally together from the origin.
Also, in the vacuum pump with the first structure according to the present invention, there is provided the vacuum pump (second structure) in which the heating electromagnet and the magnetic member face each other through a gap. Thus, the gap is provided between the heating electromagnet and the magnetic member whereby the temperature control of the gas flow path may be performed by the high responsibility of the Joule""s heat generated by the heating electromagnet coil.
Furthermore, according to the present invention, there is provided a vacuum pump (third structure) in the foregoing first and second structure, in which the heating electromagnet is fixed to one of the base portion and the stator portion through a heat insulating portion for reducing heat conduction between the heating electromagnet and the one.
In the vacuum pump of the third structure, since the heating electromagnet surrounding the coil heated by the copper loss upon current supply is thermally insulated from the pump body having a large thermal capacitance by the thermal insulating portion, it is possible to prevent the generated heat of the coil from escaping except for the discharge path and to further effectively heat the discharge path.
As the above-described thermal insulating portion, it is possible to recommend to use a member made of heat insulating material disposed between the heating electromagnet and the one, a member in which a pillar-like member having a small thermal capacity is disposed only in a portion out of the interval between the heating electromagnet and the one.
According to the present invention, in the first, second and third structures, there is provided a vacuum pump (fourth structure) further comprising a heat transfer means for transferring heat generated from the heating electromagnet to the discharge path and the vacuum pump is fixed and arranged with respect to the magnetic member.
The place to which the heat generated by the above-described heat transfer means is the vicinity of the discharge path and may be the joint portion of the gas flow path formed in the base with the gas flow path formed by the rotor portion and the stator portion, the vicinity of the rotor portion and the stator portion out of the flow path of gas formed in the base, or the like. The vicinity of the discharge path is like to affect the performance of the vacuum pump, and the flow path is narrow in this area. According to the present invention, it is possible to positively prevent the sublimation of the gas molecular in this portion. It is therefore possible to avoid the damage of the member or the generation of vibration while suppressing the degradation of the performance of the vacuum pump.
In this case, it is preferable that the heat transfer means be provided within the discharge path of gas.
The above-described stator portion and the above-described base or the above-described outer sleeve portion and the base may be formed as the discrete members at the beginning and fixed together later, or formed integrally together from the origin.
In the vacuum pump with the first to fourth structures, at least one of the above-described heating electromagnet, the above-described magnetic member and the above-described heat transfer means may be disposed in the interior of the vacuum pump. Thus, it is possible to directly heat the gas and to utilize the heat generation with a high efficiency.
In order to attain the above-described second embodiment, according to the present invention, in the vacuum pump of the first to fourth structure, there is provided a vacuum pump (fifth structure) in which the heating electromagnet, the magnetic member and the heat transfer means are arranged within an interior of the vacuum pump.
When the heating electromagnet, the magnetic member and the heat transfer means are arranged in the interior of the vacuum pump, it is unnecessary to take a special countermeasure for keeping the safety aspect, and the generated heat hardly leaks to the outside so that the generated heat may be utilized with high efficiency.
The interior of the vacuum pump means the interior of the hollow portion of the outer sleeve portion, the interior of the outer sleeve portion, the surface of the stator portion, the interior of the stator portion, the interior of the rotor portion, the surface of the rotor portion, the surface of the base, and the interior of the base.
In the case where the above-described heating electromagnet and the above-described magnetic member and the heat transfer means are disposed in the interior of the vacuum pump, these components may be disposed on the surface or the interior of the components forming the flow path or the discharge path of the above-described gas as the interior of the vacuum pump. Thus, it is possible to directly heat the gas of the flow path or the discharge path and to utilize the heat generation with a high efficiency.
In the case where the heating electromagnet or the magnetic member and the heat transfer means are disposed on the surface or in the interior of the members constituting the flow path or the discharge path of the gas, it is possible to exemplify the case where, for example, the heating electromagnet or the magnetic member and the heat transfer means are disposed on the surface, facing the rotor, of the stator support member or the surface, facing the spacer, of the rotor support member in the turbo molecular pump provided with the rotor blades as the rotor and the rotor support member (rotor body) for supporting the rotor blades and provided with the stator support member (spacer or the like) for supporting the stator blades as the stator portion. Also, in the screw groove type pump in which the screw groove is formed in the surface, facing the stator, of the rotor portion or the surface, facing the rotor, of the stator portion, the heating electromagnet or the magnetic member and the heat transfer means may be disposed on the surface of the rotor and the stator where the screw groove is formed or the surface facing the surface where this screw groove is formed. Furthermore, it is possible to point out the case where they are disposed in the flow path surface constituting the discharge passage in the base and the interior of the base.
According to the present invention, in any one of the first to fifth structures, there is provided a vacuum pump (sixth aspect), in which a resistance value of the heating electromagnet is not less than 25 xcexa9.
If the resistance value of the heating electromagnet is not less than 25 xcexa9, in the case where the electric power of 100 W is fed to the heating electromagnet, the current value Ixe2x89xa62 (A). Accordingly, in the case where any non-used pin is provided in the connector terminal of the electromagnet drive cable of the magnetic bearing type vacuum pump, it is possible to utilize this non-used pin. Incidentally, since normally it is unnecessary to flow a large amount of current through the electromagnet drive cable of the magnetic bearing type vacuum pump, the value is 4 (A) at maximum. In view of the guaranteed value, it is preferable that the value is I=2 (A) or less. The resistance value of the heating electromagnet is not less than 25 xcexa9, so that the non-used pin of the connector terminal may be utilized.
According to the present invention, in any one of the first to sixth structures, there is provided a vacuum pump (seventh aspect), further comprising a temperature sensor for detecting a temperature of a flow path of the discharge path, wherein the control means controls the current supply to the heating electromagnet in response to an output of the temperature sensor.
According to the present invention, in any one of the first to seventh structures, there is provided a vacuum pump (eighth aspect), in which the heating electromagnet is electrically connected to an external power source through a switch, and the switch detects a temperature within the discharge path and interrupts connection between the heating electromagnet and the external power source by thermal expansion when the last mentioned temperature within the discharge path reaches a give temperature.
Such a switch is arranged to function as a control means so that the turning-on/off of the drive of the heating electromagnet may be automatically performed and the discharge path may be kept in a suitable environmental temperature range with a simple structure.
According to the present invention, in any one of the first to eighth structures, there is provided a vacuum pump (ninth aspect), in which the heat transfer means comprises a heat radiation portion formed into fins of the magnetic member or a heat radiation member fixed to the magnetic member made of high heat conductive material.